It won't have monthly payments but it will definitely have DLC and yearly expansions (GW1 had several expansions). They probably are making next expansion even before they have released the actual game. Maintaining servers cost a lot every year so there has to be constant sales to keep servers up and running. Doesn't matter whether those sales are from original game, DLC, expansions or even advertising but they need money every year. I doubt official GW1 servers even exist in 2013 anymore (depending on when GW2 is released).
You can't compare to other games because server costs for other game types are minimal compared to MMO's. And many of them can even use P2P (meaning that there are no official servers, your own PC works as server and client), MMO's can't use P2P for gaming. Remember, MMO's have thousands of players at the same time, other games only few.
